Transposable elements occur more frequently in autism-risk genes: Implications for the role of genomic instability in autism

Association of Relative Telomere Length and LINE-1 Methylation with Autism but not with Severity

Autism is associated with genomic instability, which is regulated by telomere length (TL) and index of global methylation (LINE-1). This study will determine relative TL (RTL) and LINE-1 methylation percentage for 69 patients and 33 control subjects to evaluate their potential role as biomarkers for autism. The results displayed a significant decrease of both RTL and LINE-1 methylation in autistic cases relative to controls (P < 0.001). Analysis of receiver operating characteristics curve revealed that both of RTL and LINE-1 methylation percentage have the ability to serve as autism biomarkers (area under the curve = 0.817 and 0.889, respectively). The statistical analysis revealed positive correlation between the two biomarkers (correlation coefficient = 0.439 and P < 0.001).

Bridging the Gap Between Environmental Adversity and Neuropsychiatric Disorders: The Role of Transposable Elements

Long regarded as “junk DNA,” transposable elements (TEs) have recently garnered much attention for their role in promoting genetic diversity and plasticity. While many processes involved in mammalian development require TE activity, deleterious TE insertions are a hallmark of several psychiatric disorders. Moreover, stressful events including exposure to gestational infection and trauma, are major risk factors for developing psychiatric illnesses. Here, we will provide evidence demonstrating the intersection of stressful events, atypical TE expression, and their epigenetic regulation, which may explain how neuropsychiatric phenotypes manifest. In this way, TEs may be the “bridge” between environmental perturbations and psychopathology.

Could Candida Overgrowth Be Involved in the Pathophysiology of Autism?

The purpose of this review is to summarize the current acquiredknowledge of Candida overgrowth in the intestine as a possible etiology of autism spectrum disorder (ASD). The influence of Candida sp. on the immune system, brain, and behavior of children with ASD isdescribed. The benefits of interventions such as a carbohydrates-exclusion diet, probiotic supplementation, antifungal agents, fecal microbiota transplantation (FMT), and microbiota transfer therapy (MTT) will be also discussed. Our literature query showed that the results of most studies do not fully support the hypothesis that Candida overgrowth is correlated with gastrointestinal (GI) problems and contributes to autism behavioral symptoms occurrence. On the one hand, it was reported that the modulation of microbiota composition in the gut may decrease Candida overgrowth, help reduce GI problems and autism symptoms. On the other hand, studies on humans suggesting the beneficial effects of a sugar-free diet, probiotic supplementation, FMT and MTT treatment in ASD are limited and inconclusive. Due to the increasing prevalence of ASD, studies on the etiology of this disorder are extremely needed and valuable. However, to elucidate the possible involvement of Candida in the pathophysiology of ASD, more reliable and well-designed research is certainly required.

Autism Spectrum Disorders: Analysis of Mobile Elements at 7q11.23 Williams-Beuren Region by Comparative Genomics

Autism spectrum disorders (ASD) are a group of complex neurodevelopmental disorders, characterized by a deficit in social interaction and communication. Many genetic variants are associated with ASD, including duplication of 7q11.23 encompassing 26-28 genes. Symmetrically, the hemizygous deletion of 7q11.23 causes Williams-Beuren syndrome (WBS), a multisystem disorder characterized by "hyper-sociability" and communication skills. Interestingly, deletion of four non-exonic mobile elements (MEs) in the "canine WBS locus" were associated with the behavioral divergence between the wolf and the dog and dog sociability and domestication. We hypothesized that indel of these MEs could be involved in ASD, associated with its different phenotypes and useful as biomarkers for patient stratification and therapeutic design. Since these MEs are non-exonic they have never been discovered before. We searched the corresponding MEs and loci in humans by comparative genomics. Interestingly, they mapped on different but ASD related genes. The loci in individuals with phenotypically different autism and neurotypical controls were amplified by PCR. A sub-set of each amplicon was sequenced by Sanger. No variant resulted associated with ASD and neither specific phenotypes were found but novel small-scale insertions and SNPs were discovered. Since MEs are hyper-methylated and epigenetically modulate gene expression, further investigation in ASD is necessary.

Brain-Enriched Coding and Long Non-coding RNA Genes Are Overrepresented in Recurrent Neurodevelopmental Disorder CNVs

Autism spectrum disorder (ASD) is a neurodevelopmental condition with substantial phenotypic and etiological heterogeneity. Although 10%-20% of ASD cases are attributable to copy number variation (CNV), causative genomic loci and constituent genes remain unclarified. We have developed SNATCNV, a tool that outperforms existing tools, to identify 47 recurrent ASD CNV regions from 19,663 cases and 6,479 controls documented in the AutDB database. Analysis of ASD CNV gene content using FANTOM5 shows that constituent coding genes and long non-coding RNAs have brain-enriched patterns of expression. Notably, such enrichment is not observed for regions identified by using other tools. We also find evidence of sexual dimorphism, one locus uniquely comprising a single lncRNA gene, and correlation of CNVs to distinct clinical and behavioral traits. Finally, we analyze a large dataset for schizophrenia to further demonstrate that SNATCNV is an effective, publicly available tool to define genomic loci and causative genes for multiple CNV-associated conditions.

Novel function of PIWIL1 in neuronal polarization and migration via regulation of microtubule-associated proteins

Background

Young neurons in the developing brain establish a polarized morphology for proper migration. The PIWI family of piRNA processing proteins are considered to be restrictively expressed in germline tissues and several types of cancer cells. They play important roles in spermatogenesis, stem cell maintenance, piRNA biogenesis, and transposon silencing. Interestingly a recent study showed that de novo mutations of PIWI family members are strongly associated with autism.

Results

Here, we report that PIWI-like 1 (PIWIL1), a PIWI family member known to be essential for the transition of round spermatid into elongated spermatid, plays a role in the polarization and radial migration of newborn neurons in the developing cerebral cortex. Knocking down PIWIL1 in newborn cortical neurons by in utero electroporation of specific siRNAs resulted in retardation of the transition of neurons from the multipolar stage to the bipolar stage followed by a defect in their radial migration to the proper destination. Domain analysis showed that both the RNA binding PAZ domain and the RNA processing PIWI domain in PIWIL1 were indispensable for its function in neuronal migration. Furthermore, we found that PIWIL1 unexpectedly regulates the expression of microtubule-associated proteins in cortical neurons.

Conclusions

PIWIL1 regulates neuronal polarization and radial migration partly via modulating the expression of microtubule-associated proteins (MAPs). Our finding of PIWIL1’s function in neuronal development implies conserved functions of molecules participating in morphogenesis of brain and germline tissue and provides a mechanism as to how mutations of PIWI may be associated with autism.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-015-0131-0) contains supplementary material, which is available to authorized users.